Method and apparatus for cooling locally heated workpieces

ABSTRACT

A method and apparatus particularly adapted to cool hardened workpieces which have been locally heated for annealing purposes. In accordance with the invention, once a workpiece has been locally heated to a temperature above its critical temperature, it is immediately passed through a cooling zone having a plurality of water nozzles disposed therealong to provide a low velocity water fog within the zone and particularly against the heated portion of the workpiece in order to cool the workpiece at a rate below the critical cooling rate and to prevent the unheated portion from being conductively heated and thereby softened.

United States Patent 191 Snyder et al.

[ METHOD AND APPARATUS FOR COOLING LOCALLY HEATED WORKPIECES [75] Inventors: James J. Snyder, Summit; Frederick A. Schuckert, Cuyahoga, both of Ohio [73] Assignee: Park-Ohio Industries, Inc.,

Cleveland, Ohio [22] Filed: Dec. 1, 1971 [21] App]. No.: 203,692

[52] US. Cl. 148/145, 148/148 [51] Int. Cl. C2ld l/42, C2ld 9/36 [58] Field of Search 148/145, 147, 148

[56] References Cited UNITED STATES PATENTS 1,824,410 9/1931 Sheehan 148/148 2,327,129 8/1943 Ronan 148/148 2,619,439 11/1952 Rennick .1 148/145 [11] 3,821,037 [4 June 28, 1974 2,958,524 11/1960 Delapena et a1 148/145 3,090,712 5/1963 Berry 148/145 3,108,913 10/1963 Sommer 148/145 Primary Examiner-W. W. Stallard Attorney, Agent, or Firm-Meyer, Tilberry & Brody [57] ABSTRACT A method and apparatus particularly adapted to cool hardened workpieces which have been locally heated for annealing purposes. In accordance with the invention, once a workpiece has been locally heated to a temperature above its critical temperature, it is immediately passed through a cooling zone having a plurality of water nozzles disposed therealong to provide a low velocity water fog within the zone and particularly against the heated portion of the workpiece in order to cool the workpiece at a rate below the critical cooling rate and to prevent the unheated portion from being conductively heated and thereby softened.

1 Claim, 4 Drawing Figures METHOD AND APPARATUS FOR COOLING LOCALLY HEATED WORKPIECES This application pertains to the art of heat treating and more particularly to annealing steel workpieces.

The invention is particularly applicable t annealing selected portions of small hardened workpieces, such as ball studs for use in the automotive industry, and will be described with particular reference thereto; however, it will be appreciated that the invention has broader applications and may be used in other instances where it is desired to anneal only a portion of a previously hardened workpiece.

The ball studs are first hardened so as to provide improved wear surfaces thereover. However, it is generally necessary to machine certain areas of these previously hardened ball studs in order to obtain the desired finished surface conditions. These finished surface conditions usually include threaded areas for interconnecting the ball studs into a final assembly within an automobile steering linkage. As the ball studs have already been hardened, it is necessary to soften those areas which necessitate further machining.

Heretofore, this softening has been accomplished by heating that portion of a ball stud which requires further machining into the austenitizing range (approximately l,350F. for steel) and then slowly cooling to effect annealing. However, even though only a portion of the ball stud was directly heated, additional sections of the unheated portions were indirectly heated by conduction heating thus resulting in an undesired softening of these additional sections.

It was also found that unless cooling of the heated portion was retained at a rate less than the critical cooling rate for the type of material involved, the heated portion would be re-hardened during the cooling state. Early attempts to overcome this particular problem gave rise to the use of high velocity air streams which were directed against the locally heated areas, but this approach did not satisfactorily solve the re-hardening problem in view of the relatively fast cooling rate caused thereby. If low velocity air streams were used, however, there was not a sufficient volume thereof to effect cooling at a rate which would prevent annealing of the ball stud portions adjacent the directly heated portion.

The present invention contemplates anew and improved method and apparatus which overcomes the above referred problems and others and provides a method and apparatus for cooling locally heated workpieces which is simple to use, provides consistent reabove method of heat treating. The apparatus compiece having a known heating transformation and a prises a heating zone including means for heating the first portion to a temperature above the transformation temperature and a cooling zone adjacent the heating zone including means for cooling the first portion to a temperature below the transformation temperature at a rate less than the critical cooling rate.

In accordance with a limited aspect of the present invention, the cooling means comprises a plurality of fluid supply nozzles spaced along a separate cooling zone for supplying an atomized cooling fluid throughout the cooling zone. The principal object of the present invention is the provision of a method and apparatus for cooling locally heated workpieces.

Another object of the present invention is the provision of a method and apparatus for cooling locally heated workpieces which assures cooling of the locally heated portion at a rate less than the critical cooling temperature.

Another object of the present invention is the provision of a method and apparatus for cooling locally heated workpieces which substantially eliminates undesired conduction heating of the unheated workpiece portions.

Still another object of the present invention is the I provision of a method and apparatus for cooling locally heated workpieces which is simple and economical to employ.

The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein: v

FIG. 1 is a view of a typical workpiece which is desired to be locally heat treated; v

FIG. 2 is a generally schematic plan view of the apparatus employed in practicing the concepts of the, subject invention;

FIG. 3 is a cross sectional view taken along lines 3+3 in FIG. 2; and,

FIG. 4 is a cross sectional view taken along lines 4-4 in FIG. 2.

Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred embodiment of the invention only and not for purposes of limiting same, the FIGURES show a steel ball stud A which, again, is a typical workpiece of the type in which it is desired to locally heat treat a portion thereof in a heat treating apparatus" B.

More specifically, ball stud A includes an enlarged bulbous portion 10 having extending outwardly therefrom a shank comprised of upper and lower shank portions 12,14. As seenin FIG. 1 and for purposes of the following description, it is desired. to locally heat treat or anneal lower shank portion 14 longitudinally over distancea. Reference will hereinafter be made to heating one of these workpieces using the method and apparatus which will hereinafter be more fully disclosed. It will be understood that any of a plurality of other sizes and configurations of workpieces could also be locally heat treated in a similar fashion.

Heat treating apparatus B includes supply area 20, heating zone 22, cooling zone 24, unloading area 26 and transfer table 28. Supply area 20 is comprised of a hopper and sorter device 30 which is considered conventional and designed to sort and retain a plurality of ball studs A in a desired feeding position for continuously feeding along a feed chute 32, also considered conventionah'into a desired oriented association with transfer table 28.

Transfer table 28 is comprised of a generally circular table portion 40 mounted for rotation about its center on a mounting shaft 42. Mounting shaft 42 may be connected to table portion 40 in any convenient means and may also include drive means for rotating the shaft and table portion to effect movement of workpieces through the apparatus as desired. This drive means is not shown and may comprise any convenient means such as an electric motor with the necessary gearing, as is conventional with industrial machinery. The table portion includes a plurality of work stations 44 at spaced intervals therearound to extend generally radially outward from the outer circumferential edge thereof. For ease of illustration, only three work stations 44 are shown in FIG. 2, it being understood that these stations are spaced conveniently entirely around the table portion. Each work station 44 is comprised of a pair of clamp arms 46,48 conveniently pivotally mounted on pivot points 50 and having disposed therebetween a drive cylinder 52 in order to selectively effect movement of the clamp arms of each station be tween an opened condition and a closed, workpiece clamping condition. In order to securely retain workpieces A in the work stations, workpiece receiving recesses 54,56 are disposed in clamp arms 46,48, respectively. These recesses are, and for the ball stud A employed as an example in this disclosure, of a generally semi-circular configuration. Drive cylinder 52 may be of any convenient type and, in the preferred embodiment, comprises a pneumatic cylinder having the necessary inlets and outlets (not shown) for operative purposes. Other means, such as springs, could be employed in place of these cylinders.

Heating zone 22 includes a channel-type induction heating coil generally designated 60 which is comprised of longitudinally extending legs 62,64 and cross-over legs 66,68. It should be noted that legs 62,64 have a generlly arced configuration so as to be coextensive with the generally circular workpiece pass defined by table portion 40. Further, legs 62,64 are disposed as is conventional in order that a workpiece A passing therebetween will be placed in an inductive coupling relationship therewith. The channel-type induction heating coil also includes leads 70,72 with a high frequency generator generally designated 74 connected thereto and the coil may be water cooled as is conventional in the art.

Cooling zone 24 includes a pair of spaced apart rows 80,82 of fluid supply nozzles disposed to define a workpiece pass 83 therebetween which is coextensive with the workpiece path defined by table portion 40. These nozzles may be of a commercially available type and include small fluid release orifices therein which will provide an atomized or fine mist-like fluid flow throughout the zone during operation. Atomized, as used hereinafter, refers to a condition whereby minute fluid particles are suspended in air. Each nozzle in rows 80,82 includes fluid supply lines 84,86 respectively (FIG. 4) which, in turn, are connected to a fluid supply manifold generally designated 88. In the preferred embodiment, water is the cooling fluid employed as it is known to be an excellent cooling fluid for this type of work and is also readily available at low cost. The water introduced into the manifold passes through supply lines 84,86 and out of the nozzles along rows 80,82. In accordance with the present invention, the nozzles employed not only provide an atomized spray or fog, they also provide the atomized spray or fog at a low velocity. In order to retain the spray or fog within cooling zone 24, a shroud generally designated is provided which may be constructed from any convenient material such as sheet metal or the like. Shroud 90 includes a top wall 92, opposed side walls, 94,96 and a bottom wall 98 adjacent the lower end of side wall 96.

In the preferred embodiment of the invention, unloading area 26 comprises a workpiece removal track 100 which permits the individual workpieces A to travel therealong to a storage area when released from their individual work stations 44 as will hereinafter be more fully described.

In using the apparatus as hereinabove described, a plurality of the ball studs are placed in supply area 20 for proper orientation'therein. They are then singularly fed down feed chute 32 into association with a work station 44 spaced along table portion 40. The work station spaced immediately adjacent feed chute 32 has its cylinder 52 moved to the extended position so that clamp arms 46,48 are placed in a spaced apart relationship. As a ball stud passes down feed chute 32 and between the clamp arms, cylinder 52 is retracted so as to clamp the ball stud therebetween in recesses 54,56. The feed chute is positioned such that, and with reference to the ball stud shown in FIG. 1, the workpiece is clamped at upper shank portion 12 immediately below bulbous portion 10. Transfer table 28 is then rotated to move counterclockwise in the view of FIG. 2 in direction b and additional ball studs (not shown) are located in each of the subsequent work stations 44 as they pass by supply area 20 and feed chute 32 as hereinabove described. When the ball stud reaches heating zone 22, and with reference to FIG. 3, lower shank portion 14 passes between longitudinally extending conductor legs 62,64 and is inductively heated thereby as is conventional. It should be noted in that FIGURE that the workpiece is clamped so as to overhang table portion 40 in such a manner so that lower shank portion 14 extends below the bottom of the table portion. As it is desired to anneal lower shank portion 14 over area a, it is desired to heat this portion to a temperature of at least approximately 1,350F. It will be appreciated that in annealing, the workpiece is heated into the austeni tizing range and subsequently cooled at arate below the critical cooling rate in order that the workpiece will not be re-hardened. Although it will be further understood that the austenitizing range for steel workpieces will vary upon the carbon content of the workpiece itself, a temperature of approximately 1,350F. may be generally employed for the most commonly used steels for workpieces of this type. Once area a has been heated to the austenitizing range, the area has, in effect, been softened from the hardened condition. The specifics of effecting heating to 1,350F. may be controlled by the speed the workpiece travels through the heating zone and by the inductor design and operation. As these 'criterial are conventional in nature, they are not more fully described herein.

Once heated, and as transfer table 28 moves further in direction 12, the ball stud enters the cooling zone which is best shown in FIGS. 2 and 4. Without this cooling zone, the heated lower shank portion 14 will effect heating of the upper shank portion 12 and bulbous portion by conduction heating which is undesired since any heating thereof into the austenitizing range similarly causes softening. As the upper shank portion and bulbous portion are to be utilized in engagement with a receiving socket, it is of practical necessity that they remain in the hardened condition. As the workpiece enters the cooling zone, rows 80,82 of fluid nozzles cause the fine spray or fog to be directed against lower shank portion 14. This spray has two purposes. First, is to draw off the heat of the lower shank portion so that upper shank portion 12 and bulbous portion 10 will not be heated by conduction to a temperature within the austenitizing range. Second is to control the cooling rate of the lower shank portion so that it willcool at a rate slower than the critical cooling rate and thereby be retained in a soft or annealed condition. The fluid or fog mist is directed against the heated portion at low velocity since a high velocity spray would cause rapid cooling and subsequent undesired re-hardening as previously explained. For the above reasons, it may be desirable to cause the spray or fog to flow from the nozzles throughout the entire cooling zone 24 defined by shroud 90 and although the fog is directed generally toward the heated lower shank portion 14, the specific focus is not of critical importance since thefog generated by the nozzles will envelope the entire cooling zone. The cooling zone is of sufficient length to permit workpiece cooling to an extent whereby any further undesirable transformations will not occur within lower shank portion 14 once it leaves the zone in the soft or annealed condition.

As transfer table 28 continues to rotate in direction b and the workpiece passes from the cooling zone, it travels toward unloading area 26. When the workpiece reaches workpiece removal track 100, cylinder 52 is energized to expand to open clamp arms 46,48and release the ball stud A therefrom to travel down track for storage or further processing such as, for example, machining threads into the lower shank portion.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon the reading and understanding of this specification. It is my intention to include all such modification and alteration insofar as they come within the scope of the appended claims or the equivalents thereof.

Having thus described our invention, we now claim:

1. A method of annealing the shaft portion of a previously hardened workpiece formed from a metal having a known heating transformation temperature and a known critical cooling rate and said workpiece having a shaft portion with a central axis whereby said shaft portion is softened while the remainder of said workcooled zone directing an atomized cooling fluid against said shaft portion in a direction generally transverse to said axis whereby said shaft portion is cooled below said transformation temperature at a rate less than said critical cooling rate. 

